Asbestos is a collection of natural occurring crystalline fibrous silicate minerals.
The formation of these would mostly have been through a metamorphic process, i.e. rock subjected to conditions of heat and pressure to produce the fibrous crystalline form.
Asbestos minerals generally appear in veins up to 10 to 15 cm in thickness with the fibres running perpendicular to the vein.
There are two main types of asbestos – Amphibole and Serpentine.
- Amphiboles are members of a group of minerals known as chain silicates.
- There are five existing in the fibrous or asbestiform habit, the three less common as: asbestos actinolite, asbestos anthophllite and asbestos tremolite.
- The more commercially known (asbestos grunerite) amosite (brown) and crocidolite (blue) are known in non-fibrous form as grunerite (amosite) and riebeckite (crocidolite).
- Amphibole fibres appear very straight, harsh, and relatively brittle. They are also less soluble than chrysotile.
- Serpentine is a member of a group of minerals known as sheet or layer silicates.
- There is only one existing in the fibrous or asbestiform habit, known as chrysotile.
- The non-asbestos forms of chrysotile are lizardite and antigarite
- Chrysotile fibres appear curled and flexible, also silky and much softer than amphibole fibres.
All within these groups have been prized for their tensile strength and imperviousness to abrasion, vermin, acids and bases, salt, dust, frost and of course, fire.
Why was asbestos used?
The main properties which have made asbestos so useful are:
- Thermal stability and incombustibility
- Thermal insulation (low thermal conducting)
- Electrical insulation
- Tensile strength
- Chemical durability and acid resistance
Being a relatively cheap product was also a reason as to why it was used and why the health issues associated with manufacturing and working with asbestos fibres were ignored and obscured by manufactures of asbestos products. For further information, see our Asbestos in buildings page.